@media screen and (min-width:750px) {
    html {
        font-size: 75px !important;
    }
}

* {
    box-sizing: border-box;
}

body {
    min-width: 320px;
    max-width: 750px;
    /* flexible 给我们划分了 10 等份 */
    width: 10rem;
    margin: 0 auto;
    line-height: 1.5;
    font-family: Arial, Helvetica;
    background: #f2f2f2;
}

html,
body {
    width: 100%;
    height: 100%;
}